Regulation of the CYP27B1 5′-flanking region by transforming growth factor-beta in ROS 17/2.8 osteoblast-like cells

The biologically active form of vitamin D, 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃), regulates osteoblast proliferation and differentiation. Production of 1,25(OH)₂D₃ is catalysed by the enzyme 25-hydroxyvitamin D₃-1α-hydroxylase (CYP27B1). Though highly expressed in the kidney, the CYP27B1 gene is also expressed in non-renal tissues including bone. It is hypothesised that local production of 1,25(OH)₂D₃ by osteoblasts plays an autocrine or paracrine role. The aim of this study was to investigate what factors regulate expression of the CYP27B1 gene in osteoblast cells. ROS 17/2.8 osteoblast cells were transiently transfected with plasmid constructs containing the 5′-flanking sequence of the human CYP27B1 gene fused to a luciferase reporter gene. Cells were treated with either parathyroid hormone (PTH), 1,25(OH)₂D₃, transforming growth factor-beta (TGF-β) or insulin-like growth factor-1 (IGF-1) and luciferase activity was measured 24 h later. The results showed that 1,25(OH)₂D₃ did not alter expression of the reporter construct, however treatment with PTH, IGF-1 and TGF-β decreased expression by 18, 53 and 58% respectively. The repressive action of TGF-β was isolated to the region between −531 and −305 bp. These data suggest that expression of the 5′-flanking region for the CYP27B1 gene in osteoblast cells may be regulated differently to that previously described in kidney cells.     

Purification and characterization of mouse CYP27B1 overproduced by an Escherichia coli system coexpressing molecular chaperonins GroEL/ES

The expression of mouse CYP27B1 in Escherichia coli has been dramatically enhanced by coexpression of GroEL/ES. To reveal the enzymatic properties of CYP27B1, we measured its hydroxylation activity toward vitamin D3 and 1alpha-hydroxyvitamin D3 (1alpha(OH)D3) in addition to the physiological substrate 25(OH)D3. Surprisingly, CYP27B1 converted vitamin D3 to 1alpha,25(OH)D3. Both 1alpha-hydroxylation activity toward vitamin D3, and 25-hydroxylation activity toward 1alpha(OH)D3 were observed. The Km and Vmax values for 25-hydroxylation activity toward 1alpha(OH)D3 were estimated to be 1.7 microM and 0.51 mol/min/mol P450, respectively, while those for 1alpha-hydroxylation activity toward 25(OH)D3 were 0.050 microM and 2.73 mol/min/mol P450, respectively. Note that the substrate must be fixed in the opposite direction in the substrate-binding pocket of CYP27B1 between 1alpha-hydroxylation and 25-hydroxylation. Based on these results and the fact that human CYP27A1 and Streptomyces CYP105A1 also convert vitamin D3 to 1alpha,25(OH)D3, 1alpha-hydroxylation, and 25-hydroxylation of vitamin D3 appear to be closely linked together.     

Monocyte-derived cells express CYP27A1 and convert vitamin D3 into its active metabolite

CYP27A1 catalyses hydroxylations in the biosynthesis of bile acids and the bioactivation of vitamin D3. We investigated the expression of CYP27A1 in human monocytes, monocyte-derived macrophages, and dendritic cells on mRNA and protein levels as well as its enzymatic activity in comparison with the expression of CYP27B1 and CYP24A1. Macrophages showed a strong expression of CYP27A1, whereas monocytes and dendritic cells expressed low levels of CYP27A1 mRNA. Immunohistochemistry revealed CYP27A1 and CYP27B1 protein expression in macrophages. Accordingly, macrophages converted vitamin D3 into the active metabolite 1,25(OH)2D3. Dendritic cells also metabolized vitamin D3 although to a lesser extent. This could be due to the high expression of CYP24A1, the enzyme that degrades 25(OH)D3 and 1,25(OH)2D3. Our results show that macrophages and dendritic cells are capable to perform both hydroxylation steps of the vitamin D3 metabolism suggesting a possible role of local 1,25(OH)2D3 synthesis by myeloid cells in the skin and gut.     

CYP27A1 inhibits bladder cancer cells proliferation by regulating cholesterol homeostasis

CYP27A1, an enzyme involved in regulating cellular cholesterol homeostasis, converts cholesterol into 27-hydroxycholesterol (27-HC). The relationship between CYP27A1 and cell proliferation was studied to determine the role of CYP27A1 in bladder cancer. The expression of CYP27A1 in three bladder cancer cell lines (T24, UM-UC-3 and 5637) were assessed by qRT-PCR and Western blotting, and cells with stable CYP27A1 expression were generated by lentiviral infection. Cell proliferation was detected by MTT assays, colony formation assays and a tumor xenograft model in vitro and in vivo, and the intracellular 27-HC and cholesterol secretion levels were detected by enzyme-linked immunosorbent assays (ELISA). The results revealed that CYP27A1 expression was downregulated in androgen receptor (AR)-positive T24/UM-UC-3 cells compared with AR-negative 5637 cell. After CYP27A1 expression was restored, cell proliferation was inhibited in vitro and in vivo because much more intracellular 27-HC was produced in the CYP27A1-overexpressing cells than in the control cells. Both T24 and UM-UC-3 cells treated with 27-HC showed similar results. In addition, CYP27A1/27HC could reduce the cellular cholesterol level in both T24 and UM-UC-3 cells by upregulating ATP-binding cassette transporters G1 and A1 (ABCG1 and ABCA1) through Liver X receptors (LXRs) pathway and downregulating low-density lipoprotein receptor (LDLR) expression. These findings all suggest that CYP27A1 is a critical cholesterol sensor in bladder cancer cells that may contribute significantly to bladder cancer proliferation.     

Fyn mediates transforming growth factor-beta1-induced down-regulation of E-cadherin in human A549 lung cancer cells

Transforming growth factor-beta (TGF-β) signaling positively contributes to the regulation of tumor metastasis. However, the underlying molecular mechanisms are less well defined. We here show that Fyn, a member of Src family tyrosine kinases, plays a critical role in mediating TGF-β1-induced down-regulation of E-cadherin in human A549 lung cancer cells. Blockade of Fyn with siRNA knockdown or ligand-binding defective mutant significantly lowered the ability of TGF-β1 to repress E-cadherin expression. Furthermore, our results demonstrated that Fyn facilitates TGF-β1-mediated suppression of E-cadherin through p38 kinase-dependent induction of Snail. Collectively, our findings identify a Fyn-p38-Snail cascade as a new signaling pathway mediating oncogenic TGF-β function.     

miR-27b synergizes with anticancer drugs via p53 activation and CYP1B1 suppression

Liver and kidney cancers are notorious for drug resistance. Due to the complexity, redundancy and interpatient heterogeneity of resistance mechanisms, most efforts targeting a single pathway were unsuccessful. Novel personalized therapies targeting multiple essential drug resistance pathways in parallel hold a promise for future cancer treatment. Exploiting the multitarget characteristic of microRNAs (miRNAs), we developed a new therapeutic strategy by the combinational use of miRNA and anticancer drugs to increase drug response. By a systems approach, we identified that miR-27b, a miRNA deleted in liver and kidney cancers, sensitizes cancer cells to a broad spectrum of anticancer drugs in vitro and in vivo. Functionally, miR-27b enhances drug response by activating p53-dependent apoptosis and reducing CYP1B1-mediated drug detoxification. Notably, miR-27b promotes drug response specifically in patients carrying p53-wild-type or CYP1B1-high signature. Together, we propose that miR-27b synergizes with anticancer drugs in a defined subgroup of liver and kidney cancer patients.     

Regulation by estrogen through the 5'-flanking region of the transforming growth factor alpha gene.

Expression of transforming growth factor alpha (TGF alpha) mRNA and protein can be stimulated by estrogens such as 17 beta-estradiol (E2) in estrogen-responsive rodent and human breast cancer cells. To ascertain if E2 can directly regulate TGF alpha expression through the 5'-flanking region of the human TGF alpha gene, E2-responsive MCF-7 or ZR-75-1 human breast cancer cells or E2-nonresponsive MDA-MB-231 breast cancer cells were transiently transfected with a plasmid containing an 1140-base pair (bp) Sac-I fragment of the TGF alpha 5'-flanking region ligated to the chloramphenicol acetyltransferase (CAT) gene. Cells that were transfected and subsequently treated with physiological concentrations of E2 (10(-11)-10(-8) M) for 24 h exhibited a 2- to 10-fold increase in CAT activity. The E2 stimulation of CAT activity was dose-dependent with an increase first found at 10(-10) M E2. The increase in CAT activity could be detected within 24-36 h after the addition of E2. There was no significant change in CAT activity in transiently transfected MDA-MB-231 cells as mediated through the TGF alpha 5'-flanking region after E2 treatment. MCF-7 cells were also transiently transfected with different fragments of the TGF alpha 5'-flanking region ligated to the luciferase gene. In the absence of E2 treatment, no detectable luciferase activity was found.(ABSTRACT TRUNCATED AT 250 WORDS)     

Metabolism of vitamin D by human microsomal CYP2R1

The activation of vitamin D requires 25-hydroxylation in the liver and 1alpha-hydroxylation in the kidney. However, it remains unclear which enzyme is relevant to vitamin D 25-hydroxylation. Recently, human CYP2R1 has been reported to be a potential candidate for a hepatic vitamin D 25-hydroxylase. Thus, vitamin D metabolism by CYP2R1 was compared with human mitochondrial CYP27A1, which used to be considered a physiologically important vitamin D(3) 25-hydroxylase. A clear difference was observed between CYP2R1 and CYP27A1 in the metabolism of vitamin D(2). CYP2R1 hydroxylated vitamin D(2) at the C-25 position while CYP27A1 hydroxylated it at positions C-24 and C-27. The K(m) and k(cat) values for the CYP2R1-dependent 25-hydroxylation activity toward vitamin D(3) were 0.45microM and 0.97min(-1), respectively. The k(cat)/K(m) value of CYP2R1 was 26-fold higher than that of CYP27A1. These results strongly suggest that CYP2R1 plays a physiologically important role in the vitamin D 25-hydroxylation in humans.     

AH receptor antagonist inhibits constitutive CYP1A1 and CYP1B1 expression in rat BP8 cells

The BP8 variant of the 5L rat hepatoma cell line is completely devoid of aryl hydrocarbon receptor (AHR) and is a useful model to examine AHR function. Previous studies showed that BP8 cells, when transfected with mouse AHR, exhibit induction of a plasmid-based reporter even in the absence of exogenous ligands. We transfected BP8 cells with full-length human AHR and found that presence of the AHR alone was sufficient to induce substantial CYP1A1 and CYP1B1 mRNA without any exogenous AHR ligand. An AHR antagonist, 3,4-dimethoxyflavone, inhibited CYP1A1 and CYP1B1 expression in a dose-dependent manner. When we transfected BP8 cells with a mutated human AHR that is defective in ligand binding, expression of CYP1A1 and CYP1B1 was diminished but not abolished. Inhibition by the AHR antagonist along with the diminished response to the mutated AHR indicates that BP8 cells contain some agent that acts as an agonist ligand for the AHR.     

CYP1B1酶抑制剂的最新研究进展

细胞色素P450(CYP)1B1是CYP1家族的一个亚型,参与多环芳香烃等前致癌物的代谢活化,并在17-β-雌二醇诱导的乳腺癌发生与发展过程中起到了关键性作用。该酶在肿瘤组织中的特异性高表达及在肿瘤细胞耐药中的作用,也已被大量研究证实。该酶的特异性分布及在肿瘤发生与发展中的重要地位,使得它成为抗肿瘤药物研究中的新靶点。其抑制剂研究,在肿瘤预防及克服肿瘤耐药方面具有重要意义。本文综述了近二十年来发现的CYP1B1酶的强选择性抑制剂,同时分析了它们的构效关系,对发现具有肿瘤预防及逆转肿瘤耐药作用的酶抑制剂提供了理论依据。     

Polymorphisms of the CYP1B1 gene have higher risk for prostate cancer

Various carcinogenic factors including estrogen metabolites play a role in malignant transformation. These metabolites are formed in part, as a result of the hydroxylation activity of cytochrome P450 (CYP) 1B1. Variant forms of this enzyme have been shown to enhance its activity, and thus, we hypothesize that single nucleotide polymorphisms of the CYP1B1 gene can be a risk factor for prostate cancer. To test this hypothesis, the genetic distribution of six different CYP1B1 polymorphisms at intron 1 (C-->T), codon 48 (C-->G), codon 119 (G-->T), codon 432 (C-->G), codon 449 (C-->T), and codon 453 (A-->G) was analyzed in 117 prostate cancer samples and 200 healthy normal subjects from a Japanese population. Results of these experiments demonstrate that the genotype at codon 119 is significantly different between prostate cancer patients and controls (P<0.001). The odds ratio of genotype T/T compared to G/G (reference) was calculated as 4.02 with a 95% confidence interval of 1.73-9.38. All other codons, except 453, showed polymorphisms but were not significantly different between cancer patients and controls. No association was found between stage and grade of cancer with any of the polymorphic sites. This is the first report that demonstrates the polymorphism at codon 119 of CYP1B1 to be associated with prostatic carcinogenesis. These results are important in understanding the role of CYP1B1 polymorphisms in the pathogenesis of prostate cancer.     

Marked change in the balance between CYP27A1 and CYP46A1 mediated elimination of cholesterol during differentiation of human neuronal cells

Cholesterol metabolism in the brain is distinct from that in other tissues due to the fact that cholesterol itself is unable to pass across the blood-brain barrier. Elimination of brain cholesterol is mainly dependent on a neuronal-specific cytochrome P450, CYP46A1, catalyzing the conversion of cholesterol into 24(S)-hydroxycholesterol (24OHC), which is able to pass the blood-brain barrier. A suitable model for studying this elimination from human neuronal cells has not been described previously. It is shown here that differentiated Ntera2/clone D1 (NT2) cells express the key genes involved in brain cholesterol homeostasis including CYP46A1, and that the expression profiles of the genes observed during neuronal differentiation are those expected to occur in vivo. Thus there was a decrease in the mRNA levels corresponding to cholesterol synthesis enzymes and a marked increase in the mRNA level of CYP46A1. The latter increase was associated with increased levels of CYP46A1 protein and increased production of 24OHC. The magnitude of the secretion of 24OHC from the differentiated NT2 cells into the medium was similar to that expected to occur under in vivo conditions. An alternative to elimination of cholesterol by the CYP46A1 mechanism is elimination by CYP27A1, and the product of this enzyme, 27-hydroxycholesterol (27OHC), is also known to pass the blood-brain barrier. The CYP27A1 protein level decreased during the differentiation of the NT2 cells in parallel with decreased production of 27OHC. The ratio between 24OHC and 27OHC in the medium from the cultured cells increased, by a factor of 13, during the differentiation process. The results suggest that progenitor cells eliminate cholesterol in the form of 27OHC while neurogenesis induces a change to the CYP46A1 dependent pathway. Furthermore this study demonstrates that differentiated NT2 cells are suitable for studies of cholesterol homeostasis in human neurons.     

Enhanced Invasive and Metastatic Potential Induced by Transforming Growth Factor-β1 Might be Correlated with Glutathione-S-transferase-π, Cofilin and Heat Shock Protein 27 in SGC-7901 Gastric Cancer Cells

In our previous study, we found that the transforming growth factor （TGF）-β1 enhanced the metastatic and invasive potential of gastric cancer cells. Proteomics was employed in this study to further illustrate the underlying molecular mechanisms. After two-dimensional electrophoresis, image analysis, spot identification, protein identification and database analysis, three proteins, namely, glutathione-S-transferase-π （GST-π）, cofilin and heat shock protein 27 （HSP27）, were found to be up-regulated in TGF-β1 treated SGC-7901 cells. The findings were further confirmed by Western blot analysis. These results suggested that GST-π, cofilin and HSP27 might participate in enhanced invasive potential induced by TGF-β1.     

Comparison of genomic and cDNA sequences of guinea pig CYP2B18 and rat CYP2B2: absence of a phenobarbital-responsive enhancer module in the upstream region of the CYP2B18 gene

Potential mechanisms were investigated whereby CYP2B18, a cytochrome P450 gene exhibiting high constitutive expression but only low levels of phenobarbital-inducibility in the guinea pig liver, may be differentially regulated versus the highly inducible rat CYP2B2 gene. To comparatively assess potential regulatory sequences associated with CYP2B18, a guinea pig genomic library was screened enabling isolation of the CYP2B18 gene. The genomic screening process resulted in the identification of at least four closely-related CYP2B18 genes, designated here as CYP2B18A-D. Of these isolates, CYP2B18A exhibited sequence identical to that of the CYP2B18 cDNA. Further, the deduced amino acid sequence of the CYP2B18 cDNA was identical to that of N-terminal and internally-derived peptide sequences obtained in this investigation from CYP2B18 protein isolated from guinea pig liver. Genomic structural sequences were derived for CYP2B18A, together with the respective 5'-upstream and intronic regions of the gene. Comparison of the CYP2B18A and CYP2B2 gene sequences revealed the lack of repetitive LINE gene sequences in CYP2B18A, putative silencing elements that effect neighboring genes, although these sequences were present in both 5'-upstream and 3'-downstream regions of CYP2B2. We determined that the phenobarbital-responsive enhancer module was absent from the 5'-upstream region as well as the intronic regions of CYP2B18A gene. We hypothesize that the compromised phenobarbital inducibility of CYP2B18A stems from its lack of a functional phenobarbital responsive enhancer module.     

Effect of overexpressing fibroblast growth factor 2 protein isoforms in osteoblastic ROS 17/2.8 cells

Fibroblast growth factor-2 (FGF-2) is made by osteoblasts and modulates their function. There are high molecular weight (HMW) protein isoforms of FGF-2 that have nuclear localization sequences and a low molecular weight (LMW) 18 kDa FGF-2 protein that is exported from cells. Since FGF-2 is a trophic factor and potent mitogen for osteoblasts, the goal of this study was to utilize targeted overexpression of FGF-2 as a novel means of assessing different FGF-2 isoforms on osteoblastic cell viability and proliferation. Either LMW or HMW human Fgf2 cDNAs were cloned downstream of 3.6 kb alpha1(I)-collagen 5' regulatory elements (Col 3.6). A set of expression vectors, called Col3.6-Fgf2 isoforms-IRES-GFPsaph, capable of concurrently overexpressing either LMW or HMW FGF-2 isoforms concomitant with GFPsaph from a single bicistronic mRNA were built. Viable cell number in ROS 17/2.8 cells stably transfected with Vector (Col3.6-IRES-GFPsaph) versus each of the Col3.6-Fgf2-IRES-GFPsaph constructs were compared. In the presence of 1 or 10% serum, DNA synthesis was increased in cells expressing any isoform of FGF-2 compared with vector. However, cells transfected with HMW isoform had augmented DNA synthesis in 1 or 10% serum compared with cells expressing either ALL or LMW FGF-2 isoforms. A neutralizing FGF-2 antibody significantly reduced the mitogenic response in cells harboring ALL or the LMW FGF-2 isoforms but did not block the mitogenic effect of cells harboring the HMW isoforms. In summary, overexpression of any isoform of FGF-2 protein increased viable cell number and OB proliferation in the presence of low or high concentrations of serum. However, the HMW/nuclear isoforms preferentially mediate augmented OB proliferation. We conclude that differential expression of FGF-2 proteins isoforms is important in modulating OB function.     

肿瘤坏死因子α对ROS17/2.8细胞甲状旁腺素受体的下行调节

肿瘤坏死因子α(TNFα)是激活的单核巨噬细胞分泌的蛋白质,分子量17kD。其多功能性和选择性抑制肿瘤细胞生长的作用受到高度重视。我们的实验表明:TNFα(3×10~(-10)-1×10~(-7)mol/L)能显著降低大鼠成骨肉瘤细胞株ROS17/2.8的甲状旁腺素(PTH)受体总结合率,比对照降低7.47-37.45％,且与TNFα的浓度呈正相关。时间曲线显示,TNFα作用时间越长,受体总结合率降低越明显。Scatchard作图表明PTH受体数目降低而其亲和力无显著变化。细胞周期分析显示,TNFα(3.83×10~(-10) mol/L作用3天)能抑制S期DNA合成。可见TNFα通过减少PTH受体数目以调节骨代谢。同时通过抑制DNA的合成以调节骨细胞的增殖。